The present invention relates to conveyor belts for granular material and the like which may have a U-shaped upper reach and which can negotiate turns in a horizontal direction. In the past, belts of this type have been devised employing centrally-located cables to transmit the required belt tension and "sinusoidal" waves or flutes molded in the edges of the belt to accommodate elongation of shortening of the edges during a turn. That is, the flutes are designed to fold or unfold as required on a turn. Such flutes, however, add to the cost of the mold in which the belt is formed; and wet material tends to stick in the grooves on the working side and drop out on the return run to cause excessive "carry-back" or spillage problems. Additionally, when the belt runs over the drive drum, the flutes must elongate in an amount about twice the average edge elongation, resulting in fatigue failures of the elastomers which give a very limited life to the belt.
In U.S. Pat. No. 4,061,223, a stretchable belt conveyor designed for horizontal turns is disclosed in which a U-shaped conveyor belt is provided with reinforcing members extending transversely of the belt and spaced apart longitudinally of the belt. Elastic stretchable material is provided between the reinforcing members to permit pre-stretching the belt such that the edges remain in tension when the belt passes around curves and thereby maintains the molded shape of the belt in horizontal and vertical curves. The belt described in the aforesaid patent employs longitudinally-extending reinforcing members such as steel cables located in the central portion of the belt. The belt is described as being pre-stretched; however, no means is shown to enable pre-stretching, and particularly controlled pre-stretching, of the belt with the cables embedded therein.
In copending application Hoover Ser. No. 69,664, filed Aug. 24, 1979, and the specification of which is incorporated herein by reference, a belt conveyor is provided which eliminates the necessity for flutes at the edges of the belt and which is stretched so that the edges remain in tension when the belt passes around horizontal curves. In one embodiment, pre-stretching of the belt is achieved by riveting or otherwise fastening the belt to a chain which has loose pin connections to permit the chain to elongate and stretch the belt. That is, when the chain is attached to the conveyor belt during assembly, the chain links are, in effect, pushed together; but when the belt is installed on the conveyor, the chain links will be pulled apart by the maximum amount permitted by the loose pin connection to thereby stretch the belt to a predetermined elongation over its relaxed length.